1. Field of the Invention
The present invention relates to a binder for a fuel cell catalyst composition, a membrane-electrode assembly including the same, and a method of preparing the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel such as hydrogen, or a hydrocarbon-based material, such as methanol, ethanol, natural gas, or the like.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte membrane fuel cell is an environmentally friendly energy source for replacing conventional energy sources. It has advantages such as high power output density and energy conversion efficiency, operability at room temperature, and is able to be down-sized and closely sealed. Therefore, it can be applicable to a wide array of fields such as non-polluting automobiles, electricity generation systems, and portable power sources for mobile equipment, military equipment, and the like.
The polymer electrolyte membrane fuel cell has an advantage of high energy density, but it also has problems in the need to carefully handle hydrogen gas and the requirement of accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, or the like in order to produce hydrogen as the fuel gas.
In contrast, a direct oxidation fuel cell has a lower energy density than polymer electrolyte membrane fuel cell, but it has the advantages of easier handling of the liquid-type fuel, a low operation temperature, and no need for additional fuel reforming processors. Therefore, it has been acknowledged as an appropriate system for a portable power source for small electrical equipment.
In a fuel cell system, the stack that generates electricity substantially includes a plurality of unit cells arranged in a stacked configuration where each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). Each membrane-electrode assembly has an anode (also referred to as “a fuel electrode” or “an oxidation electrode”) and a cathode (also referred to as “an air electrode” or “a reduction electrode”) arranged on opposite sides of a polymer electrolyte membrane.
The separators not only work as passageways for supplying the fuel required to the anode and for supplying oxygen to the cathode, but also as conductors serially connecting the anode and the cathode in the membrane-electrode assembly. The electrochemical oxidation reaction of the fuel occurs at the anode and the electrochemical reduction reaction of oxygen occurs at the cathode, thereby producing electricity, heat, and water due to the transfer of the electrons generated during this process.